A multi-stage centrifugal pump assembly according to the preamble is known from EP 2 505 842 A1, which is designed such that a self-priming behavior is achieved with only a small quantity of delivery fluid. The centrifugal pump assembly described there has proven its worth, but requires a certain start-up time for the self-priming process.
From DE 44 15 157 A1, it is counted as belonging to the state of the art, with a multi-stage centrifugal pump, to lead back the delivery fluid during the suction phase by way of opening a non-return valve. Moreover, an air separator is provided, so that the air located in the assembly, during the suction phase, can be replaced by fluid which is stored in a chamber of the pump, by which means a self-priming of the pump can be ensured.